Radar apparatuses generally detect target objects (e.g., aircrafts and ships) by capturing reflection waves of discharged radio waves, and displays the detected target objects on a display screen. With radar apparatuses installed in, for example, ships, it is required to suppress influence of mutual interference between the radar apparatus of a ship concerned and the radar apparatus of another ship caused by a radio wave outputted from the other ship existing in the surroundings of the ship concerned. As one of methods of suppressing such influence of the mutual interference between the radar apparatuses, stagger triggering disclosed in, for example, Patent Document 1 (JP3561497B) is known. Staggering is for changing a transmission interval of a pulse signal based on an arbitrary pattern to avoid overlapping of reception timings of interference signals between sweeps.
Meanwhile, to prevent a collision accident between ships, it is important for an operator of the ship concerned to know the position of another ship existing in the surroundings of the ship concerned and an approaching speed of the other ship to the ship concerned. Here, the approaching speed indicates a radial element of a relative speed of the other ship to the ship concerned. As one of methods of calculating the approaching speed of the other ship, there is a pulse pair method (also referred to as self-correlation method). The pulse pair method is a method of calculating a complex self-correlation coefficient of a complex reception signal in a transmission cycle and, based on the result, calculating the approaching speed of the other ship. The pulse pair method can estimate the approaching speed in a shorter period of time compared to an echo trail function that displays a track of the other ship in an image, and Automatic Radar Plotting Aids (ARPA) that calculates the speed of the other ship based on signal intensities of reflection waves obtained in a plurality of scans.